EP2865854B1 - Device and method for reliable starting of ORC systems - Google Patents

Description

Field of invention

The invention relates to a thermodynamic cycle device, in particular an organic Rankine cycle device, comprising: a working medium; an evaporator for evaporating the working medium; an expansion machine for generating mechanical energy with expansion of the evaporated working medium; a condenser for condensing and possibly subcooling the working medium, in particular the working medium expanded in the expansion machine; and a pump for pumping the condensed working medium to the evaporator when the thermodynamic cycle device is in operation. The invention also relates to a method for starting such a thermodynamic cycle device.

State of the art

An ORC system consists of the following main components: a feed pump that conveys the liquid working medium to the evaporator with a high pressure increase, an evaporator in which the working medium is evaporated, an expansion machine in which the high-pressure steam is expanded and thereby generates mechanical energy which can be converted into electrical energy via a generator, and a condenser in which the low-pressure steam from the expansion machine is liquefied. The liquid working medium is returned to the system's feed pump from the condenser via a possible storage tank (feed tank) and a suction line.

During the start-up process, the working medium should be present in sufficient quantities in the suction line of the pump or in the feed tank, so that the pump has sufficient medium available during the entire start-up.

A second condition for the trouble-free delivery of working medium by the pump is a sufficient flow height of the fluid (working medium) applied to the pump. The flow height (NPSH) is a parameter which, in addition to the geodetic flow height, is also influenced by the thermodynamic state of the working medium, which can be explained as follows. If the subcooling (the distance to the boiling point) of the fluid at the pump inlet is not sufficiently high, the fluid can briefly evaporate at the pump inlet. This phenomenon can damage the pump and lead to partial or complete stoppage of the flow. One speaks of cavitation. The distance to the boiling pressure of the fluid at the inlet of the pump is referred to as the flow height. One parameter for quantifying this is the NPSH value (Net Positive Suction Head). A distinction is made between required, pump-specific (NPSH _r ) and adjacent (NPSH _a ) flow height, whereby the applied NPSH _a value is dependent on several system and operation-specific parameters (temperature, pressure due to geodetic flow height, saturation pressure, inert gas partial pressure, whereby the inert gas partial pressure is a additional partial pressure of a non-condensing gas, which can also be present in the circuit) is dependent. For safe operation of the pump, the applied NPSH _a value must always be above the required NPSH _r value.

Cavitation is a challenge especially for circulatory systems such as an ORC. Here, liquid condensate has to be _{pumped with little or no distance to the boiling point and consequently a low NPSH a} value. Since the required NPSH _r value is determined by the pump design, it can only be influenced to a limited extent and it must be ensured in terms of process technology at every point of operation that the applied NPSH _a value does not fall below the required value.

If an ORC system is shut down, e.g. by eliminating / switching off the heat source or by an emergency shutdown of the system, there may be an uncontrolled distribution of the working medium in the system (e.g. in an expansion machine, horizontal pipes or liquid bags), whereby the working medium does not flow to the feed tank. This can lead to insufficient working medium for the feed pump for the entire start-up process Available. The start-up process includes filling the evaporator, evaporating the working medium and thereby building up pressure, starting the expansion machine and starting the condensation and thus backflow of working medium to the feed pump.

The unfavorable distribution of the working medium and the associated difficult or even impossible start-up is a known problem for which there are various proposed solutions according to the prior art. In EP 2 613 025 A1 (System and methods for cold startup of rankine cycle devices) an orderly distribution of the working medium by suddenly opening a valve and "flushing out" of system parts with accumulations of liquid working medium is proposed. For this, however, one or more valves are required as additional components. In EP 2 345 797 A2 (Fluid feedback pump to improve cold start performance of organic rankine cycle plants) the working medium is pumped to the right places in the system by means of additional pumps. Here, too, additional components in the form of pumps are necessary to guarantee a reliable start of the system.

The prior art also teaches that steam lines must always be laid with a downward slope towards the condenser / feed container. This means that the evaporator must be located at the highest point and that when the system is idle, condensate flows through the condenser towards the feed tank. However, with the compact design of ORC systems, this is difficult or impossible to implement, especially if a maximum overall height is to be adhered to. Even if the evaporator is housed at the highest point, which would result in the automatic collection of the working medium in the condenser / feed container, the problem of system states with insufficient flow height NPSH _a as described above would not be eliminated.

The two listed disclosures from the prior art, however, cannot solve another problem: When starting up the ORC system, a situation can arise in which the feed pump and possibly also its supply line are at a higher temperature than the working medium that is sucked in from the condenser or as the working medium condensing in the condenser. The condenser, which serves as a heat sink in the circuit, can become coldest when it is not running Place in the system, e.g. when the external condenser is installed outside in air at cold outside temperatures and a pump located in a machine housing / building, which is tempered to a higher temperature than the outside temperature. Due to the large heat transfer surfaces present in the condenser or due to the dwell time of the medium in the condenser, the pump can at times have a higher temperature than the condenser, even if the ambient temperatures of the pump and condenser are the same. Thus there is an increase in temperature from the condenser to the feed pump and this reduces the flow head at the pump inlet (NPSH _a ). As a result, the pump cavitates and no working medium is conveyed. This prevents the system from starting and can damage the pump. Even after the temperature of the feed pump, supply line and condenser has been equalized, especially in the case of compact systems without large height differences and thus geodetic flow height, the flow height NPSH _a then applied can be lower than the necessary flow height NPSH _r , which in turn results in cavitation.

The problem of cavitation in ORC systems is known and, according to the disclosure in DE 10 2009 053 390 B3 be dissolved, for example, by adding inert gas to a feed container / condenser.

The document FR 2 985 767 A1 discloses a controller for a Rankine cycle system. WO 2011/057724 A2 discloses a thermodynamic machine and a method of operating it. WO 2008/031716 A2 discloses a steam cycle with improved energy efficiency. WO 2012/021881 A1 discloses the pressure control of a capacitor in a Rankine cycle, particularly in an ORC. WO 2006/131759 A2 discloses the lubrication of an expander wherein the liquid phase of the working fluid contains a lubricant. WO 2010/029905 A1 discloses a device for utilizing waste heat using a Rankine cycle.

In summary, the following can be stated as the motivation for the present invention. To start up an ORC system safely, there must be sufficient working medium with a sufficient flow height at the system's feed pump. In an ORC circuit it can be at a standstill or at bad controlled shutdown of the system result in a maldistribution of liquid working medium, which prevents a start-up due to a lack of medium in front of the feed pump. In addition, a disadvantageous temperature distribution can occur in the working medium circuit, for example the working medium in the feed area of the feed pump could be warmer than at the coldest point in the system. Due to the low flow height at the pump in this state, cavitation of the pump can occur. This prevents the system from starting reliably. In colder weather, a cold system state can also prevent the system from starting up. For example, the viscosity of the working medium or another medium present in the circuit, such as a lubricant, can increase, which can impair the delivery of the medium through the feed pump.

Description of the invention

The object of the invention is to at least partially overcome the disadvantages described above.

This object is achieved by a device according to claim 1.

It is advantageous here that a lead height sufficient for trouble-free starting of the pump is provided when the thermodynamic cycle device is started up. The closed circuit (with shut-off devices that could prevent the circulation not being closed when the system is at a standstill) is constructed in such a way that the fluid in the circuit flows through gravitational forces to the evaporator without additional drive. When the system is started from standstill, heat is applied to the evaporator so that it is the warmest component in the system. The working medium contained therein is evaporated and possibly also overheated and the resulting steam heats all parts of the system located above the evaporator. If liquid medium has accumulated in other parts of the system (e.g. in an expansion machine, horizontal pipes or bags of liquid), it is evaporated as a result of the heating and then condenses at the coldest point in the system. The coldest point in the system is usually the condenser. If this is not the case at standstill, the condenser can be controlled as the coldest point by regulating the heat sink can be set (e.g. start of cooling on the condenser). The working medium flows from the condenser as a template to the feed pump. The geometric arrangement is chosen (difference in height) so that the condensate can flow to the evaporator by gravity (difference in density between vapor and liquid). A natural circulation is created, which sets an independent order of the liquid working medium. This means that liquid working medium is collected in the low-lying part of the system (including in front of the pump) and that before the pump is started, there is sufficient working medium with a sufficient flow height in front of the pump.

An evaporator located lower than the condenser and possibly also lower-lying pipelines represent a possibility for the fluid in the circuit to flow to the evaporator due to gravitational forces without additional drive.

A further development consists in that the closed circuit between the condenser and the evaporator also includes the non-started pump and / or wherein the closed circuit between the evaporator and the condenser also includes the expansion machine. In this way, if the pump is of a design that is permeable to fluid when the pump is at a standstill, the working medium can also flow in the circuit through the pump without the pump having started.

According to another development, the pump can be located at a lower height than the evaporator. Thus, the lead height can be increased further.

Another development consists in the fact that the thermodynamic cycle device can furthermore comprise a bypass valve for bypassing the expansion machine in the circuit.

According to another development, the thermodynamic cycle device can furthermore comprise a feed container for collecting the condensed working medium, the feed container being arranged in the closed circuit between the condenser and the evaporator, in particular between the condenser and the pump.

Another development is that at least one sensor for measuring the flow height of the working medium upstream of the pump, in particular a sensor for measuring the pressure of the working medium and / or a sensor for measuring the temperature of the working medium, can also be provided.

According to another development, the thermodynamic cycle device can furthermore comprise a bypass valve for bypassing the pump in the circuit.

According to another development, the thermodynamic cycle device can furthermore comprise a recuperator for transferring thermal energy from the expanded working medium to the working medium pumped between pump and evaporator during operation of the thermodynamic cycle device, the recuperator being arranged between expansion machine and condenser; and a bypass valve for bypassing the recuperator in the circuit, wherein the bypass valve for bypassing the recuperator can in particular also be the bypass valve for bypassing the pump.

If a recuperator is used and, for example, the pipeline between the pump and evaporator runs over the recuperator in order to preheat the working medium pumped therein during operation (normal operation) of the thermodynamic cycle device with heat from the expanded evaporated working medium downstream of the expansion machine and upstream of the condenser, then it must To start the cycle device according to the invention, a bypass valve for bypassing the recuperator can be provided because otherwise no natural circulation can occur through the recuperator, which is arranged higher than the evaporator.

The above-mentioned object is also achieved by a method according to claim 9.

The method according to the invention for starting a thermodynamic cycle device according to the invention or one of its developments comprises the following steps: applying heat to the evaporator and evaporating the working medium in the evaporator, optionally also superheating the working medium in the evaporator, whereby working medium flows to the condenser; Condensation of the working medium in the condenser; Starting the pump when a predetermined Net Positive Suction Head flow height of the working medium at the pump is reached or exceeded.

The method according to the invention has the advantages that have already been described in connection with the device according to the invention.

The method according to the invention can be developed in such a way that the pump is started after reaching or exceeding a measured flow height or after a predetermined time after the start of the application of heat to the evaporator.

According to another development, the method can include the following further steps: setting the condensation temperature to a first temperature value; and setting the condensation temperature to a second temperature value after the condensed working medium with the first temperature value has reached the pump; wherein the second temperature value is greater than the first temperature value. The coldest point in the system is usually the condenser. If this is not the case at standstill, the condenser can be set as the coldest point in this way, e.g. by regulating the heat sink (e.g. starting cooling on the condenser).

According to another development, the condensation temperature can be set to a second temperature value by lowering the speed of a condenser fan and / or by lowering a cooling water mass flow or the air mass flow and / or by increasing the temperature of the cooling water mass flow or the air mass flow through the condenser. As an alternative or in addition, further measures such as the Closing the blinds or flaps of the condenser lead to an increase in the condensation temperature.

Another development is that the further steps of opening the expansion machine bypass valve before or at the same time as applying heat to the evaporator or opening the expansion machine bypass valve a predetermined first time period after applying heat to the evaporator or after reaching a predetermined first pressure the expansion machine; and closing the expansion machine bypass valve after or simultaneously with the start of the pump or closing the expansion machine bypass valve a predetermined second time period before the start of the pump or after reaching a predetermined second pressure on the expansion machine can be provided.

According to another development, the following further steps can be provided: opening the pump bypass valve and / or recuperator bypass valve before, during or for a predetermined third period of time after the evaporator is subjected to heat; and closing the pump bypass valve and / or recuperator bypass valve after, during or a predetermined fourth time period before the start of the pump.

The above-mentioned developments can be used individually or suitably combined with one another.

Further features and exemplary embodiments as well as advantages of the present invention are explained in more detail below with reference to the drawings. It should be understood that the embodiments do not exhaust the scope of the present invention. It is further understood that some or all of the features described below can also be combined with one another in other ways.

drawings

Figure 1

shows the height arrangement in a thermodynamic cycle device, in particular in an ORC system, according to the present invention.

Figure 2

shows an embodiment with combinable advantageous developments of the thermodynamic cycle device according to FIG Figure 1 .

Figure 3

shows another embodiment of the thermodynamic cycle device according to the invention.

Embodiments

Figure 1 shows a thermodynamic cyclic process device, in particular an ORC system and the vertical arrangement of the main components. The system comprises a feed pump 1, which conveys the liquid working medium with a large increase in pressure to an evaporator 2 in which the working medium is evaporated, an expansion machine 3 in which the high pressure steam is expanded and mechanical energy is generated in the process. This can be converted into electrical energy via a generator G, for example. From the condenser 4, in which the low-pressure steam from the expansion machine 3 is liquefied, the liquid working medium is returned to the feed pump 1 of the system via a possible (optional) storage container (feed container) and a suction line.

A description of the start-up process is given below and the solution to the problem by means of the described arrangement is shown.

Automatic organization of the liquid working medium: The system should start up from a standstill. First of all, the evaporator is exposed to heat (if the heat is not applied to the evaporator in an uncontrolled manner, e.g. through a permanent flow of a heat transfer medium, this must be switched on). In the evaporator, steam forms, which heats the system components, in others System parts (e.g. in expansion machines, horizontal pipes or bags of liquid), the liquid-bearing working medium evaporates and flows together with these to the condenser, where it is liquefied after a while. There is thus a shift in fluid from the evaporator to the condenser. This leads to an increase in the fluid level on the condenser side, which in turn leads to a pressure gradient from the cold condenser side to the warm evaporator side. The connection described (without closed shut-off devices) creates a flow that allows the medium to flow from the condenser to the evaporator via the pump. The route must be designed in such a way that the flow is established solely by gravity. For this, the pressure losses of the built-in components or the opening pressures of built-in valves must be taken into account.

Generation of flow height and system start: The orderly distribution of liquid medium (as described above) and collecting a sufficient amount of working medium in front of the pump does not guarantee, however, that the medium _{is present at the pump with sufficient flow height (NPSH a} ) at the start of the Allow pump. The following procedure can be used to create a sufficient advance height. By cooling the condenser (using a heat sink such as ambient air or cooling water), the condensation temperature and consequently the pressure in the condenser are initially reduced. Low temperature condensate flows from the condenser into the feed tank (if present) and then into the feed line to the pump. After some time, the fluid reaches the pump with the low condensation temperature that sets in due to the natural circulation. Now, for example by regulating the heat sink, the temperature in the condenser is raised, which also increases the pressure in the condenser. This can be done, for example, by lowering the speed of a condenser fan and / or by lowering a cooling water mass flow or the air mass flow and / or by increasing the temperature of the cooling water mass flow or the air mass flow through the condenser. Due to the colder fluid applied to the pump and the increased pressure in the condenser, the flow height applied to the pump increases. After exceeding a limit value of the flow height (NPSH _a > NPSH _r ) or after a certain, experience-based time, the pump can be started in order to begin the regular start-up process of the ORC system.

In contrast, the prior art teaches (as set out above) that steam lines must always be laid with a downward slope to the condenser / feed container.

The device according to Figure 2 includes to improve the in Figure 1 arrangement shown additional components. These and their function are described below with reference to.

Component 5 designates a bypass valve on the expansion machine 3. This bypass valve 5 via the expansion machine enables, e.g. in volumetric expansion machines, that a sufficient amount of the vapor generated in the evaporator can flow to the condenser 4. The bypass valve can also serve as an emergency shutdown valve, which in the event of danger enables the high-pressure steam to be rapidly released in front of the expansion machine. The bypass valve can, for example, be designed as a normally open solenoid valve. When starting up with the described arrangement of the components, the valve remains open and thus enables the natural circulation of the working medium. The valve is required for the function described if the amount of working medium via a stationary (or rotating) expansion machine is not sufficient for the desired natural circulation of the fluid.

The component 6 denotes a feed container. The feed tank can be required in order to provide sufficient working medium in contact with the feed pump in every operating state. It buffers the total amount of working medium and thus prevents the system from coming to a standstill in the event of loss of working medium, uneven distribution of working medium, different steam densities and thus steam masses during operation and standstill or inaccurate filling of the system. In connection with the use with inert gas, the container has a further function. It increases the volume of gas in the system. This means that the advance height can be kept relatively constant across all operating states (see also the disclosure in DE 10 2009 053 390 B3 ). When using inert gas to prevent cavitation, there is a further advantage due to the described arrangement in natural circulation. A constant circulation of the working medium, which is caused solely by the temperature difference and the resulting pressure difference between the evaporator and the condenser and regardless of the When the feed pump is in operation, the inert gas in the circuit is automatically collected in the condenser and feed tank. As in DE 10 2009 053 390 B3 described, the inert gas that is present in the feed tank increases the flow height to the pump due to its concentration-dependent partial pressure. Since the inert gas is distributed throughout the entire system by diffusion during standstill and thus the partial pressure in the feed tank drops, a cavitation-free start-up of the pump from standstill cannot always be guaranteed without a concentration of the inert gas in the feed tank through the natural circulation described, for example. This must be compensated for by a larger amount of inert gas and / or a larger feed container with a larger steam volume, so that the system can also be started safely from standstill. The required amount of inert gas can be reduced by the method described, which leads to an increasing pressure difference on the expansion machine and a higher output generated (increase in system efficiency).

The component 7 designates sensors for measuring the applied flow height (NPSH _a ). By attaching sensors (here for example pressure P and temperature T), the flow height (NPSH _a ) can be determined. This can serve as a start criterion for starting the pump during the described start-up process of the system.

Component 8 denotes a bypass valve around the feed pump. This valve 8 for bypassing the feed pump can be used in the case described in order to ensure a sufficient flow of liquid working medium from the condenser to the evaporator. This is necessary, for example, if the feed pump is impermeable to the medium due to its design (e.g. positive displacement pump) when it is at a standstill. Another reason could be the large height difference to be overcome in the pump (e.g. in vertical multistage centrifugal pumps), which prevents a natural flow. The bypass valve can be designed to be switchable or controllable. It can also be designed as a spring-loaded valve with adjustable or fixed opening and closing pressures. The valve therefore only opens when there is a certain pressure difference between the suction and pressure side of the pump and remains closed during operation of the system or the valve is up to a certain pressure difference between the pressure and suction side opens and closes automatically when operating from this certain pressure difference between pressure and suction side. The pressure difference for opening the valve must be so small that natural circulation is possible. In addition, the valve can serve as a safety valve in the event of danger. By opening the valve quickly in the event of danger, medium can flow out of the evaporator in the direction of the condenser. This prevents an excessive increase in pressure in the evaporator due to further evaporation of the working medium. In order to prevent the working medium from flowing back from the evaporator to the pump at certain operating points, for example to protect the pump from hot working medium, a check valve (not shown in the drawing) can also be used downstream of the pump.

In Figure 3 an embodiment of the thermodynamic cycle device with a recuperator 9 is shown. The recuperator 9 is used to transfer thermal energy from the expanded working medium to the working medium pumped between pump 1 and evaporator 2 during operation of the thermodynamic cycle device, the recuperator 9 being arranged between expansion machine 3 and condenser 4. Furthermore, a bypass valve 8 is provided for bypassing the recuperator 9 in the circuit, the bypass valve 8 for bypassing the recuperator 9 here also being the bypass valve 8 for bypassing the pump 1. If the pipeline between pump 1 and evaporator 2 runs over recuperator 9 in order to preheat the working medium pumped therein in normal operation of the thermodynamic cycle device with heat from the expanded vaporized working medium between expansion machine 3 and condenser 4, then the cycle device must be started according to the invention Bypass valve 8 for bridging the recuperator 9 must be open, because otherwise no natural circulation of the working medium can occur through the recuperator 9, which is arranged higher than the evaporator 2.

In summary, the following can be stated: The method according to the invention and the device according to the invention (height arrangement) ensure that the ORC can be started reliably and quickly. In the simple arrangement, the method does not require any sensors or actuators (eg valves) for a safe start. Due to the automatic distribution of the working medium in the system, the Compared to differently arranged systems (e.g. with elevated evaporator and low-lying condenser or expansion machine), the total amount of working medium in the system can be reduced, since there is always sufficient fluid in the suction line of the pump due to the non-drive arrangement of the liquid working medium. The automatic heating of the system through the natural circulation when heat is supplied ensures that the components are preheated. In cold weather, this can accelerate the start of the system and extend the service life of the components. The safe, cavitation-free start-up of the system prevents possible damage to the pump that can occur as a result of (partial) cavitation on the pump. The method can ensure a sufficient flow height for the feed pump in the start-up process. This means that other methods that would otherwise be necessary to generate a flow height can be omitted or their effect on the efficiency of the system can be reduced. Since other methods (e.g. undercooling of the condensate or the addition of inert gas) reduce the performance, the method described leads to an increase in the overall efficiency of the ORC system. The filling amount of working medium can be saved by the method described. Experience shows that the startability of ORC systems can otherwise only be guaranteed with large quantities of working medium. With prices of 20-80 € / kg, the working medium has a significant influence on the profitability of ORC systems. With smaller amounts of content, prescribed maintenance intervals can also be extended and the maintenance effort reduced (F-Gas Regulation), which can lead to significant cost reductions in operation. It should be noted, however, that the heat input into the system cannot be stopped in a self-locking manner - for example, by an overhead evaporator. Although this can be a disadvantage, for example for maintenance activities, the introduction of heat may have to be prevented by other, additional measures.

The illustrated embodiments are exemplary only, and the full scope of the present invention is defined by the claims.

Claims (14)

1. A thermodynamic cycle apparatus, in particular an organic Rankine cycle apparatus, comprising:

   a working medium;

   an evaporator (2) for evaporating and, optionally, additionally superheating the working medium;

   an expansion machine (3) for generating mechanical energy while expanding the evaporated working medium;

   a condenser (4) for condensing and, optionally, additionally subcooling the working medium, in particular the working medium expanded in the expansion machine; and

   a pump (1) for pumping the condensed working medium to the condenser when the thermodynamic cycle apparatus is in operation;

   wherein the evaporator (2) is located on a lower level than the condenser (4), such that, prior to starting the pump (1), the condensed working medium can flow from the condenser (4) to the evaporator (2) by force of gravity and the working medium can circulate in a closed circuit via the evaporator (2) and the condenser (4), whereby at least a predetermined minimum head height of the liquid working medium can be provided at the pump (1);

   characterized in that

   the thermodynamic cycle apparatus is further configured to provide the predetermined minimum head of the liquid working medium at the pump (1) by means of:

   a reduction of a pressure in the condenser (4) by cooling the condenser (4), and thereafter

   increasing the pressure in the condenser (4) by means of (i) lowering a speed of a fan of the condenser (4) and/or by means of (ii) reducing a cooling water mass flow or an air mass flow through the condenser (4) and/or by means of (iii) increasing a temperature of the cooling water mass flow or the air mass flow through the condenser (4).
2. The thermodynamic cycle apparatus according to claim 1, wherein the closed circuit between the condenser and the evaporator also comprises the pump and/or wherein the closed circuit between the evaporator and the condenser also comprises the expansion machine.
3. The thermodynamic cycle apparatus according to one of the claims 1 to 2, wherein the pump is located on a lower level than the evaporator.
4. The thermodynamic cycle apparatus according to one of the claims 1 to 3, further comprising a bypass valve (5) for bypassing the expansion machine in the circuit.
5. The thermodynamic cycle apparatus according to one of the claims 1 to 4, further comprising a feed tank (6) for collecting the condensed working medium, the feed tank being arranged in the closed circuit between the condenser and the evaporator, in particular between the condenser and the pump.
6. The thermodynamic cycle apparatus according to one of the claims 1 to 5, further comprising: at least one sensor for measuring the head height of the working medium upstream of the pump, in particular a sensor (7, P) for measuring the pressure of the working medium and/or a sensor (7, T) for measuring the temperature of the working medium.
7. The thermodynamic cycle apparatus according to one of the claims 1 to 6, further comprising a bypass valve (8) for bypassing the pump in the circuit.
8. The thermodynamic cycle apparatus according to one of the claims 1 to 7, further comprising:

   a recuperator for transferring thermal energy from the expanded working medium to the working medium pumped between the pump and the evaporator when the thermodynamic cycle apparatus is in operation, the recuperator being arranged between the expansion machine and the condenser; and

   a bypass valve for bridging the recuperator in the circuit, the bypass valve for bridging the recuperator being, in combination with claim 7, especially also provided as a bypass valve for bypassing the pump.
9. A method of starting a thermodynamic cycle apparatus according to one of the claims 1 to 8, the method comprising the following steps:

   applying heat to the evaporator and evaporating the working medium in the evaporator, optionally, additionally superheating the working medium in the evaporator with non-started, whereby working medium is caused to flow to the condenser;

   condensing the working medium in the condenser with non-started pump;

   starting the pump when a predetermined Net Positive Suction Head height of the working medium at the pump is reached or exceeded.
10. The method according to claim 9, wherein the pump is started when a measured head height has been reached or exceeded, or when a predetermined period of time has elapsed after the beginning of the application of heat to the evaporator.
11. The method according to claim 9 or 10, comprising the following additional steps:

    adjusting the condensation temperature to a first temperature value; and

    adjusting the condensation temperature to a second temperature value, when the condensed working medium having the first temperature value has reached the pump;

    wherein the second temperature value is higher than the first temperature value.
12. The method according to claim 11, wherein the adjustment of the condensation temperature to a second temperature value is effected by lowering the rotational speed of a condenser fan and/or by reducing a cooling water mass flow or the air mass flow and/or by increasing the temperature of the cooling water mass flow or of the air mass flow through the condenser.
13. The method according to one of the claims 9 to 12, comprising the following additional steps:

    opening the expansion machine bypass valve prior to or simultaneously with the application of heat to the evaporator or opening the expansion machine bypass valve a predetermined first period of time after the application of heat to the evaporator or after a predetermined first pressure at the expansion machine has been reached; and

    closing the expansion machine bypass valve after or simultaneously with the starting of the pump or closing the expansion machine bypass valve a predetermined second period of time prior to starting the pump or after a predetermined second pressure at the expansion machine has been reached.
14. The method according to one of the claims 9 to 13, comprising the following additional steps:

    opening the pump bypass valve and/or the recuperator bypass valve prior to, during or a predetermined third period of time subsequent to the application of heat to the evaporator; and

    closing the pump bypass valve and/or the recuperator bypass valve after, during or a predetermined fourth period of time prior to the start of the pump.

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